1. Do now: A very keen student wants to make a 1.0F capacitor,
Rāmere, 21 Paenga-whāwhā, 2017
A very keen student wants to make a 1.0F capacitor,
using parallel metal plates 1.0mm apart in air.
What size plates are needed?

2. Learning Outcomes: Homework: 1) NZQA Kirchoff (Q1-5): please mark
Last week we covered:
LO2 - 4) Kirchoff’s laws and internal resistance
This week we are learning:
LO5 - 9) Capacitors
- in series and parallel
- time constant for charging and discharging
Homework:
1) NZQA Kirchoff (Q1-5): please mark
2) NZQA Capacitor (Q1-7): due 19 Aug

3. Practical 1: Practical 2: Change area then plate separation
Add a dielectric (e.g. wooden rulers) and calculate
Measure capacitance
Practical 2:
Connect two capacitors is parallel and verify:
Connect two capacitors in series and verify:

4. Be aware: Electrolytic capacitors: “Non-polar” capacitors:
Rāmere, 21 Paenga-whāwhā, 2017
Electrolytic capacitors:
- two rolled aluminium sheets
- when charged, a very thin
layer of Al2O3 forms on the
positive plate which acts as
the dielectric.
- called “polar” because you
must connect the terminals
the right way round
- high capacitance > 5μF
“Non-polar” capacitors:
- two rolled aluminium sheets
- with plastic or ceramic in
between as the dielectric
- smaller capacitance < 5μF
- if you connect an electrolytic capacitor with the wrong polarity, the dielectric layer becomes a conductor!